Recently, higher image quality has been demanded in color images including color liquid crystal displays. A color filter is indispensable for color display of a liquid crystal display and is an important component that determines the performance of a display. Color filters can be produced by known methods such as a dyeing method, a printing method, an ink-jet method, and a photo-resist method. In particular, the photo-resist method can easily control the spectral characteristics and allows highly fine patterning because of its high resolution and is therefore a main method for producing color filters.
In the photo-resist method, the coloring agents are generally pigments. However, the pigment has a certain particle size and is thereby accompanied by a depolarization effect (i.e., collapse of polarization) to reduce the contrast ratio of color display of a liquid crystal display. Additionally, in a liquid crystal display using a pigment, since the pigment prevents the transmission of backlight, it is difficult to enhance the brightness of a color filter. Furthermore, the pigment is insoluble in organic solvents and polymers and therefore forms a dispersion in a color resist composition. Unfortunately, the stabilization of the dispersion is difficult.
In contrast, many dyes are generally soluble in organic solvents and polymers, and an appropriately selected dye can be stably present even in a color resist composition without aggregating. Accordingly, in a color filter produced from a resist composition containing a dye as the coloring agent, the dye is dispersed in a molecular level. As a result, the depolarization effect hardly occurs, and high transmission of backlight is provided.
Until now, the use of a yellow color filter containing a monoazo dye as a coloring agent has been proposed for enabling an image to be displayed with satisfactory spectral characteristics and high contrast (see Patent Literature 1). However, in order to display a finer image, it is necessary to develop a color filter having better spectral characteristics and achieving a higher contrast ratio.
Furthermore, there are demands for improvement of coloring compounds in other fields than color filters.
One of such demands is an image-forming method employing thermal transfer recording. The thermal transfer recording forms an image by stacking a thermal transfer sheet having a coloring material layer containing a heat-transferable coloring material and an image-receiving sheet having a surface provided with a coloring material-receiving layer on a sheet-like base material and heating the thermal transfer sheet to transfer the coloring material in the thermal transfer sheet to the image-receiving sheet and thereby to perform the recording. In the thermal transfer recording, the coloring compounds contained in the transfer sheet and in the ink composition for the transfer sheet highly affect the transfer recording speed and the quality and storage stability of the recorded matter and are therefore very important materials. As the dyes used in such thermal transfer recording, methine disperse dyes such as C.I. Disperse Yellow 201, disazo disperse dyes such as C.I. Disperse Orange 13, and pyridone azo dyes have been proposed (see Patent Literature 2). However, there is even now a demand for developing a coloring compound having further enhanced characteristics such as saturation, color tone (in particular, expansion of the green gamut), and solvent solubility.